How a radio transmitter circuit mixes audio with carrier wave?
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To start off, it is not "mixing". It is "modulation". The two basic types are "AM" (amplitude) where the audio varies the amplitude of the radio carrier wave and "FM" modulation where the audio frequency varies the frequency of the radio carrier wave. I f you want to know how this is done with hardware, the is too complicated for any short answer. Read: Modulation - Wikipedia
RFI-EMI-GUY
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The transmitter oscillator creates the carrier wave (channel center) of the modulated signal. The receiver local oscillator (in a superheterodyne receiver, creates a reference for channel center that is offset by the intermediate frequency (IF) by some amount, typically 10.7 MHz in common radio designs. The IF amplifiers feed the demodulator , either an FM discriminator or AM detector. Single Sideband radios operate like AM radios with another layer of modulation and demodulation (complexity).
This mixing is called modulation of a carrier. In transmitter, the carrier is generated by an oscilator.
This is its simplest form. The two simple forms are amplitude modulation (AM) and frequency modulation (FM)
The complexities go up from there.
With digital, the simplest form is on/off keying (OOSK) commonly known as CW. this only requires an oscilator.
This is its simplest form. The two simple forms are amplitude modulation (AM) and frequency modulation (FM)
The complexities go up from there.
With digital, the simplest form is on/off keying (OOSK) commonly known as CW. this only requires an oscilator.
paulears
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There is also magic taking place. In amplitude modulation, the thing to remember is that the actual power is going up and down as the signal gets louder and softer, so silence means hardly any modulation, and the loudest signal maxes out the transmitter. As radio at the listener end is the wanted signal mixed in with all the interference - as in man made, and natural, like lightning - you don't want the wanted signal disappearing into the noise, so broadcast stations use compressors to bring up the quiet bits to near the volume of the loud bits. This makes speech appear more round and punchy - the sound the US gave to the world as 'radio'. AM is of course quite inefficient. The power is the sort of oomph, and the content - speech or music is the fine detail.
A strange effects also occurs - while you have a centre spot frequency, with the 'power' - you also get two smaller bands of energy containing the fine detail. I'm clearly oversimplifying this, by the way - but good for some research if you want). These two bands either side of the carrier carry the detail, the centre sort of operates as the railway track - and doesn't really do much we need at the receiver. Somebody had the bright idea you could remove the centre bit, the 'carrier' wave, and then recreate it at ever radio listening. It meant that the power wasted in the centre could be put into the side bands, making it more efficient. That became double side, band, suppressed carrier. DSB. They then tried removing one of the side bands too - and this became the standard for short wave communications. USB -upper side band, or lower side band USB.
The downside is a reduction in the audio bandwidth - think of it like an orchestra recording - AM has every instrument from the double basses to the piccolos. Single Side Band, with suppressed carrier doesn't have any double basses, only the high strings of the cellos, and the piccolo players vanish as do most of the flutes.
Worse though is that if you remove (for example) a carrier wave on 14.3001MHz, then the receiver has to recreate that 14.301MHz signal and mix it with the incoming sidebands to magically recreate the original. Trouble is, most receivers are not actually that accurate, or at least weren't, so the mixing went wrong and people's voices would become Micky Mouse, or turn a soprano into a bass baritone. They cured this with a knob marked RIT (receiver incremental tuning) which allows the listener to adjust the fine tuning and restore a voice more realistic to the one the other end.
So you need a carrier wave to 'launch' a signal containing the important data, speech or music, or tones and stuff, but as that process creates these phantom extra signals, you can just cut them out and use 100% of your power on the vital bit. So it's magic. You need something, but can remove it. That's pretty amazing, and was Marconi's Star Trek transporter.
This is the sort of science that bends your brain until suddenly, it doesn't. All my HF transmitters have been single side band since the first in 1980. AM is broadcast radio, like Voice of America and the BBC World Service. Yesterday I got a Xeigu HF radio and it has AM too. I tried it with my old HF Icom - and I transmitted AM for the first time in 44 years. I was amazed how close it was to FM. I should not have been surprised, because aircraft never made the change to FM like most other radio systems.
To be precise, we talk about modulation always linked to the mode - so that's the M bit. Amplitude Modulation, up and down in power and Frequency Modulation, up and down in frequency, but constant power. FM, looked at on a scope is a solid spike, and the width of the spike varies with content. AM spikes go higher and lower. AM also has one big spike, and two smaller spikes, spaced from the centre one - these are the side bands. You pick one, and reduce the other two and you have the SSB we use all the time. To wind you up even more, 14MHz and below, hams use the lower one, and above, they use the higher one as a sort of convention, but not I have noticed anymore, a rule.
We actually do have mixing in radio. It exists in most radio designs. Take one frequency, add another and the two mix in bizarre ways. The two add together in frequency terms and create a new one - the sum of the two, but they also create another lower one - the difference of the two. In practice if you are trying to create a new one, the other is a nuisance, so you then filter that one out.
In many practical applications mixing is bad! I work with radio microphones and many users with two or three channels have no issues. However they might hire in extra six they need ten, and you cannot just randomly pick frequencies because all the mixing of each transmitter mixes with the others and all sorts of phantom signals appear, often blotting out another, but changing as people move around. People like Shure and Sennheiser products lists of frequencies that can be used together without all these sums and differences causing issues. What you cannot do is remove a faulty Sennheiser and replace it with a Sony, Shure, Lectrosonic or other one on the same frequency - their receivers will work differently and mess it all up!
You were quite correct. Modulation is the mixing of one signal with another. We just steer clear of using mixing in this way, because we use 'mixing' differently. Confused? I bet!
A strange effects also occurs - while you have a centre spot frequency, with the 'power' - you also get two smaller bands of energy containing the fine detail. I'm clearly oversimplifying this, by the way - but good for some research if you want). These two bands either side of the carrier carry the detail, the centre sort of operates as the railway track - and doesn't really do much we need at the receiver. Somebody had the bright idea you could remove the centre bit, the 'carrier' wave, and then recreate it at ever radio listening. It meant that the power wasted in the centre could be put into the side bands, making it more efficient. That became double side, band, suppressed carrier. DSB. They then tried removing one of the side bands too - and this became the standard for short wave communications. USB -upper side band, or lower side band USB.
The downside is a reduction in the audio bandwidth - think of it like an orchestra recording - AM has every instrument from the double basses to the piccolos. Single Side Band, with suppressed carrier doesn't have any double basses, only the high strings of the cellos, and the piccolo players vanish as do most of the flutes.
Worse though is that if you remove (for example) a carrier wave on 14.3001MHz, then the receiver has to recreate that 14.301MHz signal and mix it with the incoming sidebands to magically recreate the original. Trouble is, most receivers are not actually that accurate, or at least weren't, so the mixing went wrong and people's voices would become Micky Mouse, or turn a soprano into a bass baritone. They cured this with a knob marked RIT (receiver incremental tuning) which allows the listener to adjust the fine tuning and restore a voice more realistic to the one the other end.
So you need a carrier wave to 'launch' a signal containing the important data, speech or music, or tones and stuff, but as that process creates these phantom extra signals, you can just cut them out and use 100% of your power on the vital bit. So it's magic. You need something, but can remove it. That's pretty amazing, and was Marconi's Star Trek transporter.
This is the sort of science that bends your brain until suddenly, it doesn't. All my HF transmitters have been single side band since the first in 1980. AM is broadcast radio, like Voice of America and the BBC World Service. Yesterday I got a Xeigu HF radio and it has AM too. I tried it with my old HF Icom - and I transmitted AM for the first time in 44 years. I was amazed how close it was to FM. I should not have been surprised, because aircraft never made the change to FM like most other radio systems.
To be precise, we talk about modulation always linked to the mode - so that's the M bit. Amplitude Modulation, up and down in power and Frequency Modulation, up and down in frequency, but constant power. FM, looked at on a scope is a solid spike, and the width of the spike varies with content. AM spikes go higher and lower. AM also has one big spike, and two smaller spikes, spaced from the centre one - these are the side bands. You pick one, and reduce the other two and you have the SSB we use all the time. To wind you up even more, 14MHz and below, hams use the lower one, and above, they use the higher one as a sort of convention, but not I have noticed anymore, a rule.
We actually do have mixing in radio. It exists in most radio designs. Take one frequency, add another and the two mix in bizarre ways. The two add together in frequency terms and create a new one - the sum of the two, but they also create another lower one - the difference of the two. In practice if you are trying to create a new one, the other is a nuisance, so you then filter that one out.
In many practical applications mixing is bad! I work with radio microphones and many users with two or three channels have no issues. However they might hire in extra six they need ten, and you cannot just randomly pick frequencies because all the mixing of each transmitter mixes with the others and all sorts of phantom signals appear, often blotting out another, but changing as people move around. People like Shure and Sennheiser products lists of frequencies that can be used together without all these sums and differences causing issues. What you cannot do is remove a faulty Sennheiser and replace it with a Sony, Shure, Lectrosonic or other one on the same frequency - their receivers will work differently and mess it all up!
You were quite correct. Modulation is the mixing of one signal with another. We just steer clear of using mixing in this way, because we use 'mixing' differently. Confused? I bet!
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He said "transmitter" not "receiver".
But I need to know the modulation difference between AM and FM. If AM means amplitude modulation, does that mean the amplitude (strength) of the carrier wave (generated by the oscillator) changes as per the audio frequency. For example, if a audio tone of 6000 Hz is feed to the radio circuit as an audio input then 50% more amplitude will be generated then a 3000 Hz tone? So, the height of the radio amplitude represents the audio frequency in AM?
Then apply for a ELECTRONICS CLASS at a TRADE SCHOOL that still teaches RF and not just Computers after your 2 year School you will have all your answers and understand how this works.
I got my Degree in 1979 alot has changed but the THEORY IS STILL THE SAME.
I got my Degree in 1979 alot has changed but the THEORY IS STILL THE SAME.
RFI-EMI-GUY
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Nope:
"Why is an oscillator required in a radio circuit?"
paulears
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You are nearly there. It is about the amount of ‘swing’ so in AM, you are correct that the modulation directly changes the carrier wave amplitude to be higher and lower. To a listener, if the transmitter modulation increases, it gets louder. Comms and broadcast do it by different amounts, but it is centered on the continuous level the carrier is set at. Your 3000Hz tone does indeed add or subtract from the level 3000 times a second. The depth is adjustable. In FM systems, the transmitter output is continuous and the 3000Hz would drag the transmit frequency down, then up. This is then called deviation, as in deviation from the average frequency. Just to confuse, there is a link to the frequency response. A typical comms FM signal might fit into a 12.5KHz channel, so the listener does not get hifi! Speech has that characteristic comms quality. Broadcast FM cannot fit in so many channels, because to allow low bass and high treble, the width of the deviation has to be increased, reducing channel count, but increasing quality.
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In either an AM or FM system, a 6000 HZ tone applied to the modulator would be reproduced at exactly same 6000 Hz tone at the demodulator. Only the recovered amplitude would vary if for example you modulate at 50% AM or FM system levels vs 100%.
To complicate things, while the tone frequency in an FM system will be recovered at same level at the companion receiver, but there is a filter applied for preemphasis of the transmitted signal and a filter for demphasis of the received signal in order to improve signal to noise ratio. So for example the transmitter will send a greater deviation at a 6000 Hz tone than at a 400 Hz tone. Note that land mobile radios cut off at about 3200 Hz while FM broadcast will transmit much higher frequency tones.
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He specifically mentioned transmitters (which also require oscillators of course). He may want to also know about receivers but did not mention that. (And note he calls "transmitters" "radio transmitters".) In fact he seemed focused on modulation. He made no mention explicitly of receivers although likely he want to know about them also.
So, in case of AM a 5kHz audio bandwidth is sampled as 5000 variations in the amplitude per second?
And for the FM a 96 kHz audio is sampled in what variations of a frequency range if the FM station is on 96 MHz?
RFI-EMI-GUY
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There was nothing incorrect in my providing that information. Not seeing your obsession with this detail.
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I have no problem with you doing that. I was just pointing out that I think he was asking something else.
RFI-EMI-GUY
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I think that you are getting a bit ahead of yourself on sampling topic which is more directed at digital processing techniques.
Trying to get useful basic information from Google is just going to muddy the waters. Now with the "AI" all bets are off as the AI is trying to accelerate "The Singularity" through cheating by blatant plagiarism and systematic "dumbing down of humans". I have an extensive library of books that often I have to refer to because the internet is simply incorrect and has no historical context.
This is a situation quickly deteriorating. Soon we will have billions of humans trained incorrectly by youtubers with less of a clue and having only ability to destroy fine automobiles by spinning them wildly into curbs or drooling over the gloved opening of a box containing a new Baofenshuii radio.
I hate to say this but you must renew your library card, or (shudder) go to the Amazon or E bay websites and spend some money.
I suggest you get a textbook like this one Electronic Communication Shrader (6th edition). I have the third edition from the 1970's and it covers all the basics in the analog world. As far as the later editions I only hope they have not watered down the basic content to make way for modern gimmickry.
6th edition
3rd edition cheap!
Electronic Communication 3rd Ed. By Robert L. Shrader 1975 HC NoDJ | eBay
This is a rare and valuable copy of the Electronic Communication 3rd Ed. By Robert L. Shrader. Published by McGraw-Hill in 1975, it is a must-have for students and professionals in the field of electronics.
www.ebay.com
This also good, a bit more subject matter, but perhaps as a second book on your book shelf.
Radio Handbook William Orr:
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A carrier (sine or cosine wave) is characterize by both an amplitude and frequency. If an audio tone of 6000Hz modulates a carrier wave (of whatever frequency that may be), the amplitude of the carrier wave now changes 6000 times a second with how much being determined by the amplitude of the modulating audio. To further explain this requires a certain amount of mathematics. Although I have a PhD in mathematics (KSU 1982) only simple trigonometry is required if you want to go deeper than a word description like the above and I do not know your level of knowing mathematics. (Nothing of this involves any connection at all with a 3000 Hz tone and thus that question will be ignored.) If you know trigonometry, the audio modulation can be represented by a low (audio) frequency cosine function *if a simple tone* otherwise the equation of the modulation is used) and the carrier frequency as a higher frequency cosine function. Now multiply these two functions. There are web sites discussing this and a very basic one is
Amplitude Modulation
Amplitude Modulation - A continuous-wave goes on continuously without any intervals and it is the baseband message signal, which contains the information. This wave has to be modulated.
www.tutorialspoint.com
When I was 15, (I'm 70 now), I was gifted a Howard Sams book "Learn Electronics Through Troubleshooting" by Wayne Lemons. No other training, class, book or school helped me more than this book. The last update was 1977, and the first edition included transistors and vacuum tubes. It explains radio theory wonderfully for people like me, as well as industrial and commercial electronics at the time.I think that you are getting a bit ahead of yourself on sampling topic which is more directed at digital processing techniques.
Trying to get useful basic information from Google is just going to muddy the waters. Now with the "AI" all bets are off as the AI is trying to accelerate "The Singularity" through cheating by blatant plagiarism and systematic "dumbing down of humans". I have an extensive library of books that often I have to refer to because the internet is simply incorrect and has no historical context.
View attachment 171564
This is a situation quickly deteriorating. Soon we will have billions of humans trained incorrectly by youtubers with less of a clue and having only ability to destroy fine automobiles by spinning them wildly into curbs or drooling over the gloved opening of a box containing a new Baofenshuii radio.
View attachment 171566
I hate to say this but you must renew your library card, or (shudder) go to the Amazon or E bay websites and spend some money.
I suggest you get a textbook like this one Electronic Communication Shrader (6th edition). I have the third edition from the 1970's and it covers all the basics in the analog world. As far as the later editions I only hope they have not watered down the basic content to make way for modern gimmickry.
6th edition
3rd edition cheap!
Electronic Communication 3rd Ed. By Robert L. Shrader 1975 HC NoDJ | eBay
This is a rare and valuable copy of the Electronic Communication 3rd Ed. By Robert L. Shrader. Published by McGraw-Hill in 1975, it is a must-have for students and professionals in the field of electronics.www.ebay.com
This also good, a bit more subject matter, but perhaps as a second book on your book shelf.
Radio Handbook William Orr:
Amazon states there are some editions available...
